This invention relates generally to medical devices and procedures, and more particularly to a method and system of deploying stent-grafts in a vascular system.
Prostheses for implantation in blood vessels or other similar organs of the living body are, in general, well known in the medical art. For example, prosthetic vascular grafts formed of biocompatible materials (e.g., Dacron® material or expanded, porous polytetrafluoroethylene (PTFE) tubing) have been employed to replace or bypass damaged or occluded natural blood vessels.
A graft material supported by a framework is known as a stent-graft or endoluminal graft. In general, the use of stent-grafts for treatment or isolation of vascular aneurysms and vessel walls which have been thinned or thickened by disease (endoluminal repair or exclusion) is well known.
Many stent-grafts, are “self-expanding”, i.e., inserted into the vascular system in a compressed or contracted state, and permitted to expand upon removal of a restraint. Self-expanding stent-grafts typically employ a wire or tube configured (e.g., bent or cut) to provide an outward radial force and employ a suitable elastic material such as stainless steel or nitinol (nickel-titanium). Nitinol may additionally employ shape memory properties.
The self-expanding stent-graft implanted at a particular location is typically configured in a tubular shape with a diameter slightly greater than the diameter of the blood vessel in which the stent-graft is intended to be used. In general, stent-grafts are typically deployed through a minimally invasive intraluminal delivery, i.e., cutting through the skin to access a lumen or vasculature or percutaneously via successive dilatation, at a convenient (and less traumatic) entry point, and routing the stent-graft through the lumen to the site where the prosthesis is to be deployed.
Intraluminal deployment in one example is effected using a delivery catheter with coaxial inner tube and sheath, arranged for relative axial movement. The stent-graft is compressed and disposed within the distal end of the sheath proximal to the distal end of the catheter and held by a stent stop or distal stent graft tip capture mechanism attached to a catheter shaft.
The catheter is then maneuvered, typically routed though a vessel until the end of the catheter (and the stent-graft contained therein) is positioned in the vicinity of the intended treatment site. The catheter shaft is then held stationary while the sheath of the delivery catheter is withdrawn. The catheter may include a stop or tip capture prevents the stent-graft from moving back as the sheath is withdrawn.
As the sheath is withdrawn, the stent-graft is gradually exposed (uncovered—released—deployed) from its proximal end. As the stent-graft is exposed it radially expands so that at least a portion of the exposed stent graft is in substantially conforming surface contact with a portion of the interior of the lumen, e.g., blood vessel wall.
In straight vessels, placement of the stent-graft is relatively straightforward. However, in complex vessels, e.g., in the aortic arch or other curved vessel, placement of the stent-graft is complicated by the tendency of the catheter to maintain a straight shape while the surround vessel curves.
More particularly, in the aortic arch, the stiffness of the delivery catheter causes the distal tip of the delivery catheter to position itself close to (if not conforming with) the vessel wall at the outer radius of curvature of the aortic arch. This offset positioning (to the outer radius) of the distal tip of the delivery system combined with the effect blood flow forces have on the stent-graft as it is deployed, results in a high likelihood that the stent graft will be deployed asymmetrically.
FIG. 1A shows a stent graft deliver catheter 20 containing a stent graft 22 substantially conforming to the outside radius of curvature of the thoracic aorta 30. As shown in FIG. 1B when the stent graft begins to deploy, the blood flow, shown by the arrow 32, causes the initial deployment of the bare spring 24 at the proximal end of the stent graft 22 to open unevenly such that the portion of the spring closer to the inner radius of the thoracic arch bends outward (from the centerline of the stent graft) and downward. As a result, the proximal end 26 of the stent graft 22 is not orthogonal to the vessel wall (see FIG. 1C).
To reiterate, as stent-graft 22 deployment begins, the blood flow (e.g., 32) catches the initially deployed springs (e.g., 24) like a sail of a sail boat and causes some springs and or stent graft portions to bend preferentially in the direction of blood flow. This causes uneven deployment such that the portion of the springs or stent graft closer to the inner radius of curvature of the aortic arch bends out (inward with respect to the radius of curvature as shown in FIGS. 1B and 1C) from the stent graft and downward when deployed high in the vessel as shown. As a result, the proximal end of the stent-graft is not deployed orthogonal to the wall of the aortic arch. To correct the initial asymmetrical deployment, the physician typically tries to reposition the stent-graft, which is generally undesirable (as vessel wall abrasion and more extensive injury may result) depending upon the particular stent graft and anatomical geometry involved. Further, due to the repositioning, additional cuff (extender) type stent-grafts may need to be deployed.
As described herein: the proximal end of the stent-graft is the end closest to the heart by way of blood flow path whereas the distal end is the end furthest away from the heart as deployed. In contrast and of note, the distal end of the delivery catheter is usually identified to the end that is farthest from the operator (handle) while the proximal end of the catheter is the end nearest the operator (handle). For purposes of clarity of discussion, as used herein, the distal end of the delivery catheter is the end that is farthest from the operator (the end furthest from the handle) while the distal end of the stent-graft is the end nearest the operator (the end nearest the handle), i.e., the distal end of the catheter and the proximal end of the stent-graft are the ends furthest from the handle while the proximal end of the catheter and the distal end of the stent-graft are the ends nearest the handle. However, those of skill in the art will understand that depending upon the access location, the stent-graft and delivery system proximal and distal designations may be consistent or opposite in actual usage. When using femoral artery access the distal ends are opposite in the device and catheter, while when using a brachial artery access they are consistent.